Rutile-based pigment and a method for the production thereof

ABSTRACT

The invention relates to a fine-particle, bright and high-coating rutile-based pigment that is devoid of any metal or reactive metal compounds relevant to mill abrasion detectable by application technology but whose grain-size in terms of particle diameters ranges from 50 to 1000 μm, for mono-, bi-, tri- or oliho-modal size distribution and a primary maximum ranges from 230 to 400 μm, wherein optionally for a bi- or poly-modal frequency distribution, a secondary maximum is less than 25% of the primary maximum between 400 and 1000 μm. The method for producing said pigment consists in treating an organic mixed-phase rutile structured oxide pigment by high-speed grinding in suspension in a ball grinding mill provided with a mechanically and chemically resistant coating until said grain-size and a substantially isometric rounded particle shape are attained. According to the invention, means for viscosity adjustment and surface conditioning of the pigment are also provided. The inventive pigment differs from prior art by improved brightness, low whiteness or low lightness, relatively high hue saturation and by extremely high covering power which is not obtainable in said class of products up to now and exhibits a low photoactivity with respect to known fine-particle rutiles. In practice no abrasivity, neither interaction of possible grinding residues with an application matrix is observed.

RELATED APPLICATION

This is a U.S. national phase continuation application of PCTapplication PCT/EP2005/008892 filed Aug. 16, 2005, published Mar. 2,2006 under WO 2006/021354, and which claims the priority of GermanApplication No. 10 2004 040 384.8, filed Aug. 20, 2004. The priorapplication is hereby incorporated by reference, in its entirety.

FIELD OF THE INVENTION

The invention relates to a fine-particle, bright, and highly opaquerutile-based pigment without the addition of impurities by reactivemetal components and to a method for the production of such pigments.

BACKGROUND OF THE INVENTION

Nickel antimony titanium yellow pigments are by nature pale yellowpigments with high opacity. Overdyeing, i.e., over-coloring, with highquality organic pigments makes it possible to obtain highly saturatedfull-tone colors with which the entire color spectrum can be covered,with the exception of blue and violet hues. This overcoloring results ina synergy between the relatively high opacity of the cost-effectivenickel antimony titanium yellow and the great color intensity of theorganic overcoloring pigments, which are generally quite expensive.

This effect can also be obtained using titanium white; however,overcoloring always leads to greater brightening, that is, to lesssaturation, due to the high whitening power of titanium white pigments.Another disadvantage of titanium white overcoloring is thephotocatalytic effect of titanium white pigments, which leads to a sharpdecrease in the light-fastness and weather-fastness of the expensiveorganic color components. Consequently, full hues based on titaniumwhite “age” some four-times faster than mixtures of the same organiccolor components with nickel antimony titanium yellow.

In the past, this decisive use of nickel antimony titanium yellow wasseldom used because the nickel titanium pigments currently available onthe market are abrasive (grain-hard and sharp-edged), have poor gloss,and are inferior in terms of covering capacity compared to titaniumwhite. Moreover, the following economic background should be considered:

Nickel antimony titanium yellows account for relatively small marketshares among titanium pigments, as the following figures demonstrate:titanium white world market: 4,000,000 tons, titanium yellow worldmarket: 20,000 tons, of which chromium antimony titanium yellow: 16,000tons, of which nickel antimony titanium yellow: 4,000 tons.

The annual tonnage of chromium antimony titanium yellow isdisproportionate to that of nickel antimony titanium yellow. As coloredpigments, nickel antimony titanium yellows offer merely anunsatisfactory option for replacing the 100,000 annual tons of leadsulfochromate and molybdate red pigments pursuant to the hazardousmaterials laws and environmental protection laws that have becomeincreasingly stringent since 1980. The reason for this is thedeficiencies, considered unchangeable, that are manifested in particularby the inadequate opacity, compared to titanium white and to chromiumand cadmium yellows and by inadequate gloss and high abrasiveness.

These three deficiencies are the result of one and the same cause,specifically a mean particle size, primarily of the nickel antimonytitanium yellow, that is too large and that is an average of 1000-2000μm in the best qualities found on the market, while the optimum opacityof a pigmentary coloring agent is attained with a particle size of 300μm and with optimized grain shape and surface. A pigment loses about 20%of its opacity when the mean particle diameter is greater than 500 μm.Finer commercial types according to the prior art are regularly slightlydoped and greatly whitened, and in addition due to their high grindingcosts expensive, highly doped, high-fired products are unknown becausethey are inconsistent in terms of color.

Surface enlargement when the mean particle diameter is 300 μm should beavoided for color pigments because they become transparent when theydrop below a particle diameter of about half the wavelength of the lightreflected by them, which is undesirable for applications for nickelantimony titanium yellow pigments. When the hardness of the particles ishigh, abrasiveness increases for spiky and sharp-edged particles. Thegoal is therefore also to produce isometric particles (rhombi) that arechamfered or have beveled flattened or rounded areas on the corners.This cannot be obtained using a coating in accordance with DE-A-2 936746 that acts in cooperation with surfactant agents such as a slip agentand which additionally requires its own processing step and the use ofauxiliary agents as the subject matter of the invention. Nevertheless,for avoiding color effects under different types of illumination(metamerism), a relatively smooth surface and also approximateuniformity of the (projected) edge lengths should be obtained; aspherical shape is unattainable under any conditions, however.

Taking the aforesaid into account, the relevant prior art shall beaddressed:

In the past, a mean particle size of 300 nm has not been reached by anymanufacturer with satisfactory results for highly doped and/or fullyannealed nickel or chromium antimony rutile yellow pigments (TiO₂<87%).Patent DE-A-3 202 158 describes in particular chromium antimony titaniumyellows. In fact, the small dopings described therein inter alia withantimony and chromium at low firing temperatures <1000° C. withsubsequent wet grinding in bead mills lead to a pigment with a narrowgrain size distribution and corresponding fineness, sometimes also dueto the softer grain of the mixed phase oxide pigments described therein.However, there are still also limits for hue creation in terms of howthe reactive iron content can assume uncontrollable amounts if anon-metallic mill with resistant lining is not used as it is inventivelyin this case. Still, with a product according to the prior art in DE-A-3202 158, increased photoactivity, and with appropriate very finegrinding, a high degree of whitening must be accepted. If iron abrasionis permitted in the milling process, the material grays and leads interalia to disturbances in PVC-based matrices. This is true even for mixedphase rutile-based oxide pigments that contain iron bound as anon-reactive component in the crystal lattice of the rutile, as inexample 3 of DE-A-3 202 158.

In accordance with the teaching of DE-A-3 202 158, a coloristicallyfavorable grain size distribution is attained when low doping,relatively low firing temperature, and wet milling are combined.However, this application does not provide any information on grain sizedistribution and specifies the type of milling only imprecisely.

In the case of titanium dioxide, synthesis during the chloride methodwith the adjustment of the TiCl₄ burner and mixing in ofagglomeration-preventing sand in the subsequent cooling and conveyingprocess has already found a practical path for adjusting optimizedparticle size distributions (d₅₀=approx. 280 nm for light of 550 nmwavelength) (see inter alia: Winkler, J: “Titanium Dioxide”, Hannover:Vincentz, 2003; ISBN 3-87870-148-9; pp. 35-37; 51-58). Although in thismethod small quantities of aluminum chloride are metered to the titaniumtetrachloride for “rutilization”, it being unresolved how many latticeplaces in the rutile are really occupied by aluminum ions, this methodis not promising e.g. using the addition of antimony and nickelchlorides to titanium tetrachloride upstream of the burner. Separationand inhomogeneous volatility of metal chlorides and metal oxychloridesprior to the lattice insertion of the metal ions is observed. A lengthyafterglow period leads to reagglomeration.

The Ishihara Company is particularly active in the prior art. This isdemonstrated by worldwide patent applications. These include forinstance EP 1 245 646 (A1, corresponds to U.S. Pat. No. 6,576,052), inwhich a fine-particle TiO₂ obtained from the chloride process, already100 to 400 μm mean grain size, is re-ground to a corresponding fineprimary grain size during a siloxane post-treatment and coating withaluminum phosphate using a jet mill. According to EP-A-1 273 555(corresponds to U.S. Pat. No. 6,616,746), the same grain fineness of theraw pigment for coating is used with multivalent alcohols and hydrolyzedamino silanes and/or aluminum hydroxide. The procedure is the same asthe foregoing. Good dispersibility of the photostabilized products isclaimed. For grinding, the pigment is comminuted after or duringaddition of the coating and stabilization reagents at a temperature of120 to 300° C. in a jet mill or a similar “fluid energy mill” thatpermits a hydrolysis reaction of the amino siloxanes and other reactivecomponents and prevents any reagglomeration during the coating process.This patent relates only to TiO₂ in rutile modification (which ispreferably formed by the additions of aluminum). After working up thebatch, the coating is principally to act in a manner that preventsagglomeration and is photostabilizing, i.e. lastingly moderates thephotocatalytic effects of the pigment.

Wet grinding of rutiles, that is also rutile yellow pigments, inhigh-intensity bead mills is prior art e.g. in accordance with DE-A-3930 098. These are sold by a number of different specialty companies.

The option provided e.g. in DE-A-4 106 003 to obtain an a priori finergrain structure and thus save a grinding process by “alloying” thefiring batch for a rutile brown pigment with small quantities of cerium,inter alia, cannot be performed with chromium and nickel titaniumpigments due to the brighter hues that are more sensitive tofluctuations in doping.

Basically many companies seem to prefer wet precipitation to the actualsynthesis of the pigment and thus create a “wet precursor” which isimprinted with the grain distribution and thus the fineness, which ismaintained even until after calcination and final fine grinding. Thehydroxyl groups on the surface of the freshly precipitated oxides andhydroxides represent a good precursor for the diffusive penetration ofthe rutile lattice, which also has numerous vacancies, with foreignmetal ions after evaporating the water above 150° C. However, the finergrain sizes possible due to the lower firing temperature are not ofreproducible color intensity. The diameter still fluctuates between 800and 1200 μm.

Proceeding from the prior art described in the foregoing, the object ofthe invention was to obtain a fine-particle, bright, and highly opaquerutile-based pigment that is distinguished by superior opacity, gloss,and lower abrasiveness. Moreover, it should have the smallest possibleor no iron content, for instance in the ppm range in any case. Moreover,the invention should provide a method with which such a pigment can beproduced in a particularly economical manner.

BRIEF DESCRIPTION OF THE INVENTION

This object is inventively attained using a fine-particle, bright, andhighly opaque rutile-based pigment that is characterized in that it hasa grain size distribution with particle diameters between 50 and 1000 μmand for mono-, bi-, tri-, or oligomodal frequency distribution has aprimary maximum between 230 and 400 μm, whereby for a bi- or multimodalfrequency distribution where necessary a secondary maximum occurs, atless than 25% of the primary maximum, between 400 and 1000 μm, inparticular between about 400 and 900 μm. It is particularly preferredwhen the claimed primary maximum is between 280 and 340 μm and/or thesecondary maximum is between 480 and 800 μm. Furthermore, it ispreferred when the mean particle diameter of the pigment is between 80and 1000 μm, in particular between 80 and 900 μm. The range of 120 to600 μm is very particularly preferred. Moreover, in individual cases itis advantageous when the pigment has an asymmetrically shaped monomodalfrequency distribution for the particle diameter with a maximum between250 and 390 μm, in particular between 280 and 340 μm.

As is consequently evident, the particle size for the type describedshould be considered an essential feature of the present invention. Thisshall be explained in greater detail in terms of the technology.Surprisingly, it has been demonstrated that the sharp grain sizedistribution must sit on a “base”, which as needed can also havesecondary maximums in the amount of up to 15%, primarily 5%. Withoutthis explanation being limiting or exhaustive, this special embodimentof a sharply asymmetrical, bi- or oligomodal grain distribution or a“deep drag” for attaining optimum brightness and saturation can betraced back to the need for providing optimum space filling in thematrix by approaching a specific portion of the pigment on the “Fullercurve”. As long as they remain the minority, the finest portions insmall diameters (150 μm<D<250 μm) themselves can certainly cause theabsorption edge of the pigment to be steeper due to stronger absorption,which likewise causes intensification of the Raleigh scattering,resulting in improved brightness.

The grain shape must also receive the required “polishing” in order tobe able to work itself optimally into a matrix, improve the gloss, andprotect the normal application tools. This can be done effectively andin the same work step in the inventive method, which will be describedin the following, by adding auxiliary agents. The grain surface isabraded, using the selected method and appropriate additives andcoatings, to the round shape, which helps to moderate the abrasivenessof the particles and to improve the flowability of highly-pigmentedpreparations in later use. The tendency of fine rutile pigments toagglomerate is now effectively addressed during creation, i.e., in thegrinding batch, which will be described in greater detail.

The invention includes in particular the following pigments: a highlydoped, fully annealed nickel antimony rutile yellow, a chromium antimonyrutile yellow that is just as highly doped and fully annealed, and atitanium dioxide, preferably made of synrutile precursors, each inrutile structure, that is just annealed and only weakly doped withforeign parts.

The inventive fine-particle, bright, and highly opaque rutile-basedpigments also result in excellent gloss values. A pigment in accordancewith the invention is distinguished in that it has a 20° reflectometergloss value of at least 42 according to DIN 67 530 and a 60°reflectometer gloss value of at least 80, in particular a 20°reflectometer gloss value of at least 50, in particular 55 to 70, and a60° reflectometer gloss value of at least 83, in particular 83 to 93.The excellent covering power of the claimed pigments is particularlyvaluable. These are distinguished in that the covering power inaccordance with DIN 55 987 is greater than 100% relative to a standardrutile pigment comparison substance, in particular is greater than 110%,and in particular is between 115 and 130%. Neither dry grinding usedtoday as the state of the art nor conventional sand/bead mills aresuitable for producing the inventive pigment of the type characterized.

The present invention also proves to be valuable because it no longerhas any regular increase in remission across all wavelengths, due to thesharpness of the grain size distribution, but rather has a maximum inthe yellow range of the spectrum (about 570 to 600 μm). Thissimultaneously prevents the b* values from decreasing excessivelybecause then the brightness (that is, the non-wavelength-specificremission) would increase excessively.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become more apparentupon reference to the following Specification and annexed drawings, inwhich:

FIG. 1 is a graph showing particle sizes.

FIG. 2 is an electron microscopic view of TY70, a conventionalcommercial pigment of Ishihara.

FIG. 3 is an electron microscopic view of a conventional commercialproduct A (jet-milled);

FIG. 4 is an electron microscopic view of the inventive nickel antimonyrutile yellow pigments; and

FIG. 5 is a graph showing the nickel antimony rutile yellow products ofthe invention in the CIELab color space as compared to the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The subject matter of the present invention is also a method forproducing the pigments in accordance with the invention. It ischaracterized in that an inorganic mixed phase oxide pigment with rutilestructure is treated by means of high-speed grinding in an aqueoussuspension in an agitator ball mill with resistant lining until thegrain size distribution described in the foregoing has been attained.Preferably the grinding unit and the grinding tools have awear-resistant and inert coating. Preferably the resistant liningmaterial for the (high-speed) agitator ball mill is an inert andwear-resistant ceramic material, in particular in the form of aheat-conductive ceramic material for assisting in cooling.Alternatively, it is preferred that the resistant lining material forthe agitator ball mill is an inert and wear-resistant plastic, e.g.polyurethane.

Additional information regarding the method. It is preferred thatresistant grinding pearls with a diameter of about 0.2 to 1.7 mm, inparticular from about 0.5 to 1.2 mm, are used in the milling unit in ananalogous manner for coating. The temperature during fine grinding ispreferably between about 20 and 90° C., in particular between about 40and 60° C. Moreover, it is useful that the fine grinding is performed inthe framework of the inventive method using a recirculation method, themean dwell time of the ground material in the agitator ball mill being 4to 44 min, in particular 10 to 18 min. It is useful that thecircumferential speed of the rotor in the agitator ball mill is 5 to 19m/s, in particular 10 to 12 m/s. In addition, in the framework of theinvention the fill level is usefully planned to be advantageous. It ispreferred that the fill level of the agitator ball mill with grindingbodies is about 60 to 90 vol. %, in particular about 70 to 80 vol. %.

In an exceptional case, it is preferred that pre-comminution occursupstream of the inventive method. This usefully occurs in a ball mill,likewise made of resistant material, metal contact with the groundmaterial being largely prevented. This is one reason that iron contentis largely prevented in the inventive pigments. In other words, thismeans that the iron content is determined solely by the parameters ofthe raw materials and is thus in any case in the ppm range.

Regarding the history of the inventive method it should be stated: Afterinitial experiments with highly doped and fully annealed nickel titaniumyellow as for the teaching of DE-A-3 202 158 with high-speed agitatorball mills failed due to unsatisfactory color consistency, it wassurprisingly found that the grinding efficiency improved dramatically inconnection with chemically and mechanically resistantly lined agitatorball mills and ceramic fine grinding bodies. Preferably the liningshould be non-metallic. It could comprise plastic, but it could alsocomprise ceramic. Therefore a sharp grain size distribution with about320 nm mean particle diameter, close to the optimum, can be attainedwith relatively low grinding complexity, the grain size distributionadditionally also having a steep course that conforms to the objective.The refitting of the agitator ball mill, mentioned in the foregoing interms of the metal-free lining, was thus extremely important forconducting the new inventive wet milling method successfully. Theinventive pigments and also the inventive method have particular value,which is evidenced by numerous advantages: for instance, the grindingefficiency can be promoted using the surfactant polymers, mentioned inthe foregoing, specifically using differently substituted polysiloxanecompounds and polar substituted long-chain alkanes. The polysiloxanesprimarily effect hydrophobization of the per se polar surface of theinorganic pigment particle. During subsequent working in into nonpolarbinding agents (solvent-containing resin) or other polymer materials(polyolefins), the hydrophobization of the pigment surface leads toclearly more rapid rewetting and thus to less wear. Under the selectedgrinding conditions, highly disperse oxides of silicon or aluminum proveto be the solution to hydrodynamic problems, in addition to adjusting anoptimal ion strength and therefore viscosity with a salt of an oxygenacid of for instance sulfur or phosphorus. Using the aforesaid compoundsit is therefore possible to obtain particularly advantageouscontrollability when optimizing the inventive method.

The present invention overcomes the aforesaid deficiencies of prior artnickel antimony titanium yellow pigments and leads, optionally using amodified finish process, to yellow pigments with substantially improvedopacity and substantially improved gloss that is the equivalent of thatof titanium white; at the same time the color intensity is improvedcompared to low-doped rutiles that are annealed at lower reactiontemperatures, which is clearly evidenced in FIG. 5. In accordance withthe object, the invention thus includes a new application area forhighly doped rutile pigments.

The advantages of the inventive pigment can be depicted as follows: Itis distinguished from the prior art product by improved gloss, lowwhiteness/less brightening, relatively high color saturation, andextremely high covering power, not usable in the past in this class ofmaterial, with low photoactivity for fine-particle rutiles compared tothe prior art. Furthermore, in practice it does not demonstrate anydisadvantageous abrasivity or any interaction of any grinding residueswith the application matrix. In particular it is essentially free ofreactive metals or metal compounds, in particular reactive ironcompounds.

The known methods attain only mean particle sizes of 600 to 1200 nm,which results from the curves in enclosed FIG. 1. In the Figure, theribbed line A represents a conventional commercial product A that wasdry jet-milled, while the dashed line B represents a conventionalcommercial nickel antimony titanium yellow, “TY70”, from the IshiharaCompany, that was milled in a conventional manner by means of a bead orjet mill. The uniform solid line C represents a pigment in accordancewith the invention. It demonstrates covering power improved by 25% andsubstantially improved gloss. The type of production is described ingreater detail in the following, although it should be stated that amicromedia mill with 1.2 mm diameter grinding bodies was employed. Theuniform solid line C in FIG. 1 that represents the inventiondemonstrates a clear leap in quality compared to the products of theribbed and dashed lines. The optimum grain size distribution in terms ofthe primary maximum, between about 230 and 400 μm, is believed onereason for the improved properties observed.

As compared to the conventional product that is usually jet milled, anexample of which is shown in FIG. 3, the product made in accordance withthe invention as shown in FIG. 4 has a smaller particle size.

FIG. 5 shows the characteristics of the nickel antimony rutile yellow inthe CIELab color space (determined according to DIN 5033, Part 3). Thesolid dot is the product of the invention and the diamond the prior artproduct. As seen, the inventive products include a new color locationcompared to the products according to the prior art. This shows that theproduct of the invention is a product that differs from the prior artproducts. The invention expands the spectrum of stable pigments with ayellow hue. It is therefore of particular advantage for nickel antimonyrutile yellows that the CIELab color location has a color saturation C*of 52 to 55 at a color hue angle h of 96 to 98° according to DIN 5033.

The invention shall be explained in the following in greater detailusing various examples, although this shall not be construed as alimitation.

EXAMPLE 1 Step 1: Pre-Comminution

It is advantageous to have a conventional pre-comminution step upstreamof fine grinding in order to limit the duration of grinding. This canoccur according to the following variations, and the ground material isthen fed directly to the inventive process (these are actually processesin accordance with the prior art, which are only included for the sakeof completeness and to demonstrate the general applicability of theinvention):

Ball Mill/Roller Block

40% suspension (4 kg pigment and 6 L water) of the raw pigment is groundwith 25-mm ceramic balls on the roller block for 60 to 90 minutes.

Sand Mill:

Horizontal PU-lined sand mill with Ottawa sand or zircon silicategrinding beads (Rimax) with a diameter of 2.5 to 2.8 mm. There are 1 to2 passes with 600 to 800 kg 40% suspension per hour. The temperaturemust be kept below 60° C.

Although a jet mill for dry pre-comminution with subsequent slurrying ofthe raw pigment to the 40% suspension is very effective and does notcause any wear, it is very complex and time-consuming to manage and istherefore expensive.

Corundum disc mill: Pre-comminution of the raw pigment particles into a40% suspension has a throughput that is too low, but can be usedtrial-wise.

EXAMPLE 2 Step 2: Inventive Wet Grinding

The 10 kg of the 40% suspension of the nickel titanium raw pigment fromExample 1 are adjusted to a pH of 6-6.5 with 10% sulfuric acid, and ifnecessary adjusted to conductivity of 2000 to 2500 μS/cm by addingsodium sulfate solution, in order to obtain a stable, pumpablesuspension having a viscosity of 600-700 mPa*s. A Lehmann “FM 20” milllined with a special heat-conductive ceramic material for cooling isused.

EXAMPLE 2A Pass Grinding

The suspension is pumped through the mill 3 times, passes 1 and 2 withgrinding balls (cerium-stabilized zircon oxide balls, bulk density 3.7kg/L) 1.7 to 2.4 mm, the third pass with grinding balls 0.7 to 1.2 mm(cerium-stabilized zircon oxide balls, bulk density 3.7 kg/L) at athroughput of 600 g suspension per minute; this is equal to a dwell timeof 130 to 150 sec per pass, that is, a total dwell time of 10 min. Themill is set to a circumferential speed of 12 m/sec. The grindingtemperature is no more than 45° C.

EXAMPLE 2B Circulatory Grinding

1 pass with grinding balls (cerium-stabilized zircon oxide balls, bulkdensity 3.7 kg/L) 1.7 to 2.4 mm (72 vol. % of the grinding space), thencirculatory grinding for 30 to 60 min with a throughput of 900 gsuspension per min, which equals total dwell time of 6 to 12 min and 4to 8 theoretical passes. It is necessary to check the pH after each passor every 30 min during circulatory grinding. If the pH rises above 6.5,it must be corrected by adding sulfuric acid. The mill is set for acircumferential speed of 11 m/sec.

After 45 minutes have elapsed, 20 g (0.2%) Nuosperse 2008, a fatty aminesalt of an ethoxylated and partially phosphatized polymer oleyl alcoholare added for conditioning and grinding continues for an additional 15min. If the suspension becomes thin, the viscosity must be raised byadding no more than 50 g sodium dihydrogen phosphate, and if necessarymore additional sulfuric acid. The grinding temperature is no more than45° C.

EXAMPLE 3 Adding Additives

After fine grinding in accordance with Example 2b, the pigment is washeduntil the conductivity of the excess liquid is 500 to 800 μS/cm. Thesuspension is concentrated by means of centrifuge decanter or filterpress to a solid content of 55 to 65%. Then additional 2.5% sodiumsulfate is added to the slurry, the viscosity is adjusted to 620 Pa*swith equal parts by weight of sodium phosphate and sulfuric acid, anadditional quick pass (dwell time <60 sec) through the mill is performedwith grinding balls (cerium-stabilized zircon oxide balls, bulk density3.7 kg/L) 1.7 to 2.4 mm.

An excellently covering yellow pigment is obtained that has optimumgloss in the coating. There are no detectable differences between thepigment in accordance with the method in Example 2A and in accordancewith the method in Example 2B.

EXAMPLE 4 Adding Additives

After fine grinding in accordance with Example 2b, the pigment is washeduntil the conductivity of the excess liquid is 500 to 800 μS/cm. Thesuspension is concentrated by means of centrifuge decanter or filterpress to a solid content of 60%. Then additional 3% non-ionic, modifiedfatty acid derivative (commercial product) and 100 g “Aerosil” are addedto the slurry, and an additional quick pass (dwell time <60 sec) throughthe mill is performed with grinding balls (cerium-stabilized zirconoxide balls, bulk density 3.7 kg/L) 1.7 to 2.4 mm (same filling asbefore).

An excellently covering yellow pigment is obtained that has optimumgloss in the coating. It is not possible to detect a feared mattingeffect from the Aerosil There are no detectable differences between thepigment in accordance with the method in Example 2A and in accordancewith the method in Example 2B.

EXAMPLE 5 Adding Additives

After fine grinding in accordance with Example 2b, the pigment is washeduntil the conductivity of the excess liquid is 500 to 800 μS/cm. Thesuspension is concentrated by means of centrifuge decanter or filterpress to a solid content of 60%. Then additional 2% a [sic] polydimethylsiloxane (aqueous emulsion) is added to the slurry to reduce abrasivity,in addition 35 g “aluminum oxide C” from the Degussa Company (commercialproduct), an additional quick pass (dwell time<60 sec) through the millis performed with grinding balls (cerium-stabilized zircon oxide balls,bulk density 3.7 kg/L) 1.7 to 2.4 mm (same filling as before).

After separation, an excellently covering, bright yellow pigment isobtained that has optimum gloss in the coating. There are no detectabledifferences between the pigment in accordance with the method in Example2A and in accordance with the method in Example 2B.

EXAMPLE 6 Variations in the Auxiliary Agents

To illustrate how independent the pigment properties are in accordancewith this invention, deviating from the wording of these examples thefollowing auxiliary agents are used in variations that are reasonable toexperts in the field without this having a significantly furtherimproving effect on the result, in contrast to DE-A-2 936 746:

Modified Fatty Acid Derivatives

1. Fatty amine salt of a polymer oleyl alcohol, ethoxylated andphosphatized, and

2. Non-ionic, modified fatty acid derivative

Polysiloxane Compounds

1. With polyether group-modified siloxane

2. Alkylaryl-Modified Polysiloxane

Nanodisperse Aluminum Oxide or Silicic Acids

Aluminum oxide C (Degussa)

Aerosils

The following can be used as grinding balls:

1.7 to 2.4 mm cerium-stabilized zircon oxide balls, bulk density 3.7kg/L

0.7 to 1.2 mm cerium-stabilized zircon oxide balls, bulk density 3.7kg/L

0.6 to 0.8 mm yttrium-stabilized zircon oxide balls, bulk density 3.6kg/L

0.8 to 1.0 mm yttrium-stabilized zircon oxide balls, bulk density 2.8kg/L

2.5 to 2.8 mm zircon silicate balls, bulk density 2.4 kg/L

EXAMPLE 7 Evaluation

After filtration and drying, a bright, highly opaque, and fine-particleyellow pigment is obtained. In comparison, the pigment in accordancewith Example 4 is as follows (Table 1): TABLE I (Mean particle size andgloss) Nickel antimony Commercial Commercial rutile yellow product TY-70product A (wet-ground) from Ishihara Material (jet-milled) InventionCompany Grinding Standard type Experiment: ceramic- process jet-milledlined Lehmann “FM” Mean particle 0.66 μm 0.31 μm 0.87 μm size d₅₀ Gloss20°/ 29.2/71.1 62.5/87.9 40.9/78.6 60° (D65)

See FIG. 1 enclosed in the attachment with regard to the particle sizein the products compared in the foregoing. The described commercialproduct A was obtained according to common multistage jet-millingmethods until no more improvement could be attained. Grain shape andparticle size can be seen and compared in enclosed FIGS. 2, 3, and 4 inraster electron-microscope images. The round polished shape that isresponsible for some of the favorable application technology propertiesis evident.

EXAMPLE 8 Non-Voluntary Confirmation of Success for Inventive ImprovedNickel Antimony Titanium Yellow Pigment

The efficacy of the invention is documented primarily by the followingincident, highlighted briefly and without any disturbing effects (thepigment is also resistant to leaching), during the development of theproduct, even though it may seem to be an unorthodox example:

Pilot production began after preliminary results from Examples 1-6 wereevaluated. Because of an error in handling, small quantities of veryfine nickel antimony rutile yellow pigment traveled out of the mill intothe receptacle for the waste water basin (clear side). The pigment wasdeposited as an extremely well covering, uniform, and intensely luminouslemon yellow coating on the walls and fittings of the waste waterpreparation system. The “result” looked like it had been applied with aroller or sprayed on in a clean, covering manner. The bright greensubstrate of the building and the various pipes, fixtures, and cablesdid not have any more yellow hue nuances in the midday sunlight. Thecolor effect initially led one to think of doped bismuth vanadate oreven lead chromate, which could not be disproved without chemicalanalysis. If one is mindful that all of this occurred without auxiliaryagents, the practical value of the improvement from the inventionbecomes quite clear.

EXAMPLE 9 Variation of the Ground Substance: Other Rutile-Based Pigments

Trial as in Examples 1 and 2A, but, instead of with nickel antimonyrutile yellow, with “off-white” titanium dioxide, obtained from asynrutile using the method according to DE-A-101 03 977, which accordingto the method described therein, but in contrast to Example 3 of DE-A-3202 158, is obtained directly and does not contain any more “reactiveiron”. A batch is produced according to Examples 1 and 2A, but a“synrutile” with 97% TiO₂ is used instead of a synthetic mixed phasecolor pigment. Similarly significant improvements result, in this casewith regard to improved brightness, opacity, and gloss, which includethe use of a “synrutile” in a direct manner (i.e. without refiningmethods, using the chloride or sulfate process, that are otherwise usualfor TiO₂) for pigment applications in the sector of pastel white colors.

In the context of this invention, the qualitative evaluation furthermoreleads to the conclusion that the inventive method is applicable to allgrain-hard or highly agglomerated pigments that are based on titaniumdioxide in a rutile structure, without having to pay for theseadvantages with weak color for lack of adequate doping, with sharplyincreased photoactivity, with a significantly increased expenditure ofenergy and/or non-specific graying due to metal abrasion of the grindingaggregate.

EXAMPLE 10 Comparison of Measured Gloss Values for Commercial Product A,Inventive Nickel Antimony Rutile Yellow, and Ishihara TY70 CommercialPigment, which were Compared in the Foregoing

The measured gloss values are determined according to DIN 67 530. Analkyd melamine stoving enamel (55% solid content) was used for thetesting system. For this, 80 g resin, 20 g pigment, and 120 g glassbeads (2 mm) were weighed into a polypropylene beaker and shaken for 20minutes on a Scandex shaker. The pigmented resin was applied to a whitetesting chart (Leneta Form WH) with a wet film thickness of 200 μm usinga film drawing device (Erichsen Company, model 509 MCIII) and fired for30 min at 130° C. Then the reflectometer values were determined withstandard illuminant D 65. TABLE II (Reflectometer values) 20°reflectometer 60° reflectometer (Standard illuminant D65) value valueCommercial pigment A 29.2 71.1 Inventive product 62.5 87.9 Nickelantimony rutile yellow (300 nm) Ishihara TY70 commercial 40.9 78.3pigment

EXAMPLE 11 Determining Covering Power

Covering power was determined according to DIN 55 97 using standardlight D65 (daylight, northern hemisphere, corresponding to emissionradiation of the black body heated to 6504 K), using an oxidativelydrying alkyd resin. For this, 70 g resin, 30 g pigment, and 120 g glassbeads (2 mm) were weighed into a polypropylene beaker and shaken for 20min on a Scandex shaker. The pigmented resin was applied to black/whitecontrast cards with wet film thicknesses of 60 to 400 μm using a filmdrawing device (Erichsen Company, model 509 MCIII) with a type 421/IIErichsen Company step rake. After the resin film was dried, the colorspacing DE was determined over black and white substrates according toDIN 6174 and applied graphically against the reciprocal value of thefilm thickness at which the color spacing is DE=1. This was determinedboth for the described nickel titanium pigments and for a titaniumdioxide pigment for the rutile modification. The covering power in TableII is provided relative to titanium dioxide. The concentration of thetested pigments was less than the critical pigment volume concentration(CPVK). TABLE III (Covering power, relative to a standard titaniumdioxide rutile pigment as comparison substance) (Standard light D 65)Covering power Commercial pigment A 89% Inventive nickel antimony rutileyellow 121% pigment (300 nm) Ishihara TY70 commercial pigment 82%

1. A fine-particle, bright, and highly opaque rutile-based pigment, thathas a grain size distribution with particle diameters between 50 and1000 μm and for mono-, bi-, tri-, or oligomodal frequency distributionhas a primary maximum between 230 and 400 μm, whereby for a bi- ormultimodal frequency distribution where necessary a secondary maximumoccurs, at less than 25% of the primary maximum between, 400 and 1000μm.
 2. The pigment in accordance with claim 1, wherein the mean particlediameter is between 80 and 1000 μm, in particular between 80 and 600 μm,and/or a secondary maximum occurs, at less than 25% of the primarymaximum between, 400 and 900 μm.
 3. The pigment in accordance with claim2, wherein the mean particle diameter is between 120 and 600 μm.
 4. Thepigment in accordance with claim 1 that has an asymmetrically shapedmonomodal frequency distribution for the particle diameter with amaximum between 250 and 390 μm, in particular between 280 and 340 μm. 5.The pigment in accordance with claim 1 which is one of a nickel antimonyrutile yellow, a chromium antimony rutile yellow, or a titanium dioxidethat is in a rutile structure and that is only weakly doped with foreignmetals without graying caused by the grinding processes and withoutadhering reactive metal compounds in the application medium.
 6. Thepigment in accordance with claim 5, wherein the CIELab color location ofa nickel antimony rutile yellow has a color saturation C* of 52 to 55 ata color hue angle h of 96 to 980 in accordance with DIN
 5033. 7. Thepigment in accordance with claim 1 in accordance with DIN 67 530 usingstandard illuminant “D65” and under the trial conditions enumerated inExample 10 it has a 20° reflectometer gloss value of at least 42 and a60° reflectometer value of at least 80, in particular a 20°reflectometer gloss value of at least 50, in particular 55 to 70, and a60° reflectometer gloss value of at least 83, in particular 83 to 93,without requiring the use of auxiliary agents that remain on thepigment.
 8. The pigment in accordance with claim 1 that has a coveringpower in accordance with DIN 55 987 using standard illuminant “D65” andthe trial conditions enumerated in Example 11 is more than 100%, inparticular more than 110%, relative to a standard titanium dioxiderutile pigment as comparison substance.
 9. The pigment in accordancewith claim 7, wherein the covering power in accordance with DIN 55 987is between 115 and 130%.
 10. The method for producing a pigment inaccordance with claim 1 wherein an inorganic mixed phase oxide pigmentwith rutile structure is treated by means of high-speed grinding in anaqueous suspension in an agitator ball mill with resistant lining untilone of the grain size distributions in the foregoing claims has beenattained.
 11. The method in accordance with claim 10, wherein thegrinding unit and the grinding tools have a wear-resistant and inertcoating.
 12. The method in accordance with claim 11, wherein iron-freeand resistant grinding beads with a diameter of about 0.2 to 1.7 mm, inparticular 0.5 to 1.2 mm, are used in said grinding unit.
 13. The methodin accordance with claim 10 wherein the grinding is performed attemperatures between about 20 and 90° C., in particular between about 40and 60° C.
 14. Method in accordance with claim wherein the grinding isperformed using a recirculation method, the mean dwell time of theground material in the agitator ball mill being 4 to 44 min, inparticular 10 to 18 min.
 15. Method in accordance with claim 10 whereinthe circumferential speed of the rotor in said agitator ball mill is 5to 19 m/s, in particular 10 to 12 m/s.
 16. Method in accordance withclaim 10 wherein the fill level of said agitator ball mill with grindingbodies is about 60 to 90 vol. %, in particular about 70 to 80 vol. %.17. Method in accordance with claim 10 wherein pre-comminution occursupstream of said method in a ball mill made of resistant material andlargely prevents the ground material from coming into contact withmetal.
 18. Method in accordance with claim 17, wherein said resistantmaterial is a heat-conductive and wear-resistant material.
 19. Method inaccordance with claim 17, wherein said resistant material is aheat-conductive ceramic material.
 20. Method in accordance with claim 10wherein said resistant lining material for said agitator ball mill is aninert and wear-resistant plastic or an inert and wear-resistant ceramicmaterial.